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ATLANTA — Traces of a chemical used in rocket fuel were found in samples of powdered baby formula, and could exceed what's considered a safe dose for adults if mixed with water also contaminated with the ingredient, a U.S. government study has found.

The study by scientists at the U.S. Centers for Disease Control and Prevention looked for the chemical, perchlorate, in different brands of powdered baby formula. It was published last month, but the Environmental Working Group issued a news release Thursday drawing attention to it.

The chemical has turned up in several cities' drinking water supplies. It can occur naturally, but most perchlorate contamination has been tied to defense and aerospace sites.

No tests have ever shown the chemical caused health problems, but scientists have said significant amounts of perchlorate can affect thyroid function. The thyroid helps set the body's metabolism. Thyroid problems can impact fetal and infant brain development.

However, the extent of the risk is hard to assess. The government requires that formula contain iodine, which counteracts perchlorate's effects. The size of the infant and how much formula they consume are other factors that can influence risk.

The study itself sheds little light on how dangerous the perchlorate in baby formula is. "This wasn't a study of health effects," said Dr. Joshua Schier, one of the authors.

The largest amounts of the chemical were in formulas derived from cow's milk, the study said.

The researchers would not disclose the brands of formula they studied. Only a few samples were studied, so it's hard to know if the perchlorate levels would be found in all containers of those brands, a CDC spokesman said.

Earlier this year, the U.S. Environmental Protection Agency said it was considering setting new limits on the amount of perchlorate that would be acceptable in drinking water. A few states have already set their own limits.

The EPA has checked nearly 4,000 public water supplies serving 10,000 people or more. About 160 of the water systems had detectable levels of perchlorate, and 31 had levels high enough to exceed a new safety level the EPA is considering.